Electronic materials based on utilization of the grain boundary of semiconductor particles are hitherto known, of which one example is the voltage-nonlinear resistor element (zinc oxide varistor) composed mainly of zinc oxide. The zinc oxide varistor is an element obtainable by adding a very small quantity of Bi.sub.2 O.sub.3, CoO, MnO, Sb.sub.2 O.sub.3 or the like to zinc oxide and firing the mixture. Its voltage nonlinearity is comparable to that of a Zener diode, and its voltage nonlinearity index .alpha. is as great as 50. Since such an element is excellent in performing in high voltage absorption, it is in use for the purpose of stabilizing the voltage of electronic instrument circuits and for protecting such circuits against abnormal voltage (surge). However, such a zinc oxide varistor is low in dielectric constant .epsilon., and its dielectric loss (tan .delta.) is as great as 5-10%, so that it functions poorly as a capacitor and accordingly has been exclusively used for fulfilling the variator function.
A grain boundary layer type semiconductor porcelain capacitor is another typical example of a element in which the grain boundary of semiconductor particles is utilized. The grain boundary layer type semiconductor porcelain capacitor is an element obtainable by re-oxidizing the grain boundary of semiconductor porcelain such as barium titanate, strontium titanate or the like, or by compensating the valencies of the porcelain. The apparent dielectric constant of this type of capacitor is as high as 50,000-60,000. Since it has a dielectric loss (tan .delta.) of about 1%, it can serve as a small-sized capacitor having high capacity. However, since its voltage nonlinearity index is as small as about 1-2 and since it cannot resist an electric current higher than 1 mA, it cannot function as a varistor. Accordingly, it is exclusively in use as a capacitor.
Recently, electric and electronic instruments have come to require a very high degree of control. It is the current tendency that not only industrial instruments but also domestic ones require a very high degree of accuracy as the result of the introduction of microcomputers. Since the logic circuits of microcomputers and the like are operated by pulse signals, these circuits are easily influenced by noise. If electronic computers, banking machines, traffic control instruments and the like fall into an erroneous operation or a breakdown due to noise or surge, there can be incurred a social problem. As a counter-measure for this problem, noise filters have hitherto been employed. The term "noise" refers to an interferential voltage different from the required signal voltage which appears in operating electronic instruments. This type of noise is classified into artificially occurring noise and naturally occurring noise. Such noise has hitherto been removed by means of the so-called noise filter which is a combination of a coil and a capacitor. However, some types of artificially occurring noise and particularly that due to the circuit breakers of transmission and distribution lines, as well as some type of naturally occurring noise and particularly that due to lightning surges, have a fundamental frequency as low as about 5-20 KHz. It has been impossible to remove this low frequency noise with only the hitherto known combination of coil and capacitor. In view of this problem, there is often used a noise filter which also has a voltage nonlinearity resistor (varistor) between lines or between line and earth. Such a noise filter is effective for preventing the erroneous operation of microcomputer-controlled instruments because a wide range of noise can be removed with it. However, such a noise filter has a great number of parts inside its set, so that its cost is high and it is contrary to the current tendency toward miniaturization.